Clinical Pharmacology for Xepi
Mechanism Of Action
XEPI is an antimicrobial drug [see Microbiology].
Pharmacodynamics
Exposure-Response Relationship
The exposure response relationship for ozenoxacin following topical application has not been studied, however; a relationship is unlikely because systemic exposure following topical application is negligible [see Pharmacokinetics].
Pharmacokinetics
Absorption
Four pharmacokinetic studies were conducted in 110 patients utilizing varying strengths of ozenoxacin cream, up to 2% (twice the concentration of the marketed formulation). Three of these studies assessed systemic absorption in healthy subjects and in subjects with impetigo. These studies were conducted with either single or repeated application of up to 1 g ozenoxacin cream to intact or abraded skin (up to 200 cm2 surface area). No systemic absorption was observed in 84 of 86 subjects, and negligible systemic absorption was observed at the level of detection (0.489 ng/mL) in 2 subjects.
Distribution
Plasma protein binding of [14C]-ozenoxacin was moderate (~80 to 85%) and did not appear to be dependent on concentration. Since negligible systemic absorption was observed in clinical studies, tissue distribution has not been investigated in humans.
Elimination
Metabolism
Ozenoxacin was not metabolized in the presence of fresh human skin discs and was minimally metabolized in human hepatocytes.
Excretion
Studies have not been investigated in humans due to the negligible systemic absorption observed in clinical studies.
Microbiology
Mechanism Of Action
Ozenoxacin is a quinolone antimicrobial drug. The mechanism of action involves the inhibition of bacterial DNA replication enzymes, DNA gyrase A and topoisomerase IV. Ozenoxacin has been shown to be bactericidal against S. aureus and S. pyogenes organisms.
Resistance
The mechanism of quinolone resistance can arise through mutations of one or more of the genes that encode DNA gyrase or topoisomerase IV. Resistant organisms will typically carry a combination of mutations within gyrA and parC subunits.
Overall the frequency of resistant mutants selected by ozenoxacin is ≤10-10.
Interaction With Other Antimicrobials
Ozenoxacin has been tested in combination with 17 other commonly used antimicrobial agents against S. aureus and S.pyogenes. Antagonism interactions with ozenoxacin were observed with ciprofloxacin against S. aureus.
Antimicrobial Activity
Ozenoxacin has been shown to be active against most isolates of the following microorganisms, both in vitro and in clinical infections [see INDICATIONS]:
Gram-positive bacteria
Staphylococcus aureus (including methicillin-resistant isolates)
Streptococcus pyogenes
Clinical Studies
The safety and efficacy of XEPI for the treatment of impetigo was evaluated in two multi-center, randomized, double-blind placebo controlled clinical trials (Trial 1, (NCT01397461) and Trial 2, (NCT02090764)). Seven-hundred twenty-three (723) subjects two months of age and older with an affected body surface area of up to 100 cm , and not exceeding 2% for subjects aged 2 months to 11 years were randomized to XEPI or placebo. Subjects applied XEPI or placebo twice daily for 5 days. Subjects with underlying skin disease (e.g., preexisting eczematous dermatitis), skin trauma, clinical evidence of secondary infection, or systemic signs and symptoms of infection (such as fever), were excluded from these studies.
Overall clinical success was defined as no need for additional antimicrobial therapy of the baseline affected area(s) and absence/reduction in clinical signs and symptoms assessed at the end of therapy (Day 6-7), as follows: absence of exudates/pus, crusting, tissue warmth, and pain; and erythema/inflammation, tissue edema, and itching assessed as less than mild in Trial 1; and absence of blistering, exudates/pus, crusting, and itching/pain, and mild or improved erythema/inflammation in Trial 2. Table 2 below presents the results for clinical response at the end of therapy.
Table 2 Clinical Response at End of Therapy in Trial 1 and Trial 2 in All Randomized Subjects
|
Trial 1 |
Trial 2 |
| XEPI |
Placebo |
XEPI |
Placebo |
(N = 155)
n (%) |
(N = 156)
n (%) |
(N = 206)
n (%) |
(N = 206)
n (%) |
| Clinical success |
54 (34.8) |
30 (19.2) |
112 (54.4) |
78 (37.9) |
| Clinical failure |
98 (63.2) |
120 (76.9) |
91 (44.2) |
121 (58.7) |
| Unable to determine |
3 (1.9) |
6 (3.8) |
3 (1.5) |
7 (3.4) |
| a The success rates for ozenoxacin were significantly different than placebo in Study 1 and Study 2 (p = 0.002 and p = 0.001). |
The most commonly identified bacteria were S. aureus and S. pyogenes. Table 3 below presents the results for clinical success at end of therapy in subjects with S.aureus or S.pyogenes at baseline.
Table 3 Clinical Success at End of Therapy in Trial 1 and Trial 2 in Subjects with S. aureus or S. pyogenes
| Clinical success |
Trial 1 |
Trial 2 |
| XEPI |
Placebo |
XEPI |
Placebo |
| n/N (%) |
n/N (%) |
n/N (%) |
n/N (%) |
| S. aureus |
35/93 (37.6) |
16/98 (16.3) |
66/115 (57.4) |
36/108 (33.3) |
| S. pyogenes |
29/73 (39.7) |
7/67 (10.4) |
15/19 (78.9) |
8/20 (40.0) |